Fluid processing systems are used in the semiconductor and pharmaceutical industries (as well as in other industries) to provide a precise quantity of fluid or fluids to a processing chamber. For example, in the semiconductor industry, fluid processing systems may be used to provide precisely metered quantities of fluid or fluids to a semiconductor wafer processing chamber. In a typical fluid processing system, each of a plurality of fluid supplies are respectively coupled to a mass flow controller that is capable of providing a precisely metered amount of fluid to a common manifold. The common manifold is fluidly coupled to an inlet of the process chamber. Conventionally, the process chamber has only a single inlet to receive the flow of process fluids from the common manifold.
Sometimes dividing combined process gases equally among multiple process chambers, or among separate portions of a single process chamber, is desired. In such cases, a single outlet of the gas box may be connected to secondary flow paths. Existing flow splitters heretofore have relied on thermal or pressure sensors to measure the flow rate through each outlet channel. The output signal of these sensors is a function of the flow rate through each sensor; therefore these devices have a limited flow range. Different splitters are required to accurately split different inlet flow rates. In addition, thermal and pressure sensors drift over time, so that these devices need to be re-calibrated. Thermal or pressure sensor-based devices also require increased pressure drop to achieve a reasonable sensor signal. This increases the system pressure drop and slows the response of the gas delivery system. A sensor-based flow splitter using two control systems that will oscillate until equilibrium can be established. This can take up to ten seconds, which represents a significant delay in semiconductor processing.